Bobbin thread control means for a lock stitch sewing machine

ABSTRACT

A lock stitch sewing machine is provided with mechanism operable by a feed dog for pulling thread for stitches from a bobbin spool in amounts predetermined by the setting of a stitch length regulator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to thread handling devices for use in sewing machine and more particularly to mechanism for pulling thread from a bobbin spool in a lock stitch sewing machine.

2. Description of the Prior Art

It is known to provide a lock stitch sewing machine with means for pulling thread from a bobbin spool for use in the formation of stitches, and it is usual for such thread pulling means to supply a constant amount of thread for each stitch regardless of the length of stitch called for. However, the feeding of constant amounts of bobbin thread regardless of stitch length requirements is a disadvantage in that it may result in stitches which are too tight and cause puckering of material being sewn, or in stitches, which are inadequately locked and tend to pull out the material.

SUMMARY OF THE INVENTION

In accordance with the invention, a lock stitch sewing machine is provided with mechanism which includes fixed thread supporting means between a bobbin spool and needle, a thread engageable member mounted for movement along an arcuate path and cooperable with the fixed thread supporting means for pulling thread from the bobbin spool, an angular extension on the thread engageable member, a feed dog for moving material under the needle, stitch regulating means for moving the feed dog according to a selected length for stitches to be formed in the material, and a member affixed to the feed dog and engageable with said angular extension for causing thread to be pulled from the bobbin spool in amounts defined in accordance with the setting of the stitch regulating means.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary end elevational view partially in section of a sewing machine including bobbin thread control means according to the invention;

FIG. 2 is a top plan view taken on the plane of line 2--2 of FIG. 1 with portions broken away to better show the control means of the invention;

FIG. 3 is an exploded perspective view illustrating said bobbin thread control means;

FIGS. 4 and 5 are fragmentary end elevational views showing the operation of mechanism according to the invention during the formation of short and long stitches respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, reference character 10 designates the head end of a lock stitch sewing machine wherein a needle bar 12 is vertically reciprocable. A sewing needle 14 is affixed in the needle bar 12 for reciprocation thereby. As shown, the head end 10 of the sewing machine carries a presser bar 16, and the presser bar carries a foot 18 which is used to hold down work as it is sewn with the needle 14.

Thread 20 is supplied to the needle 14 for use in forming stitches, and a loop taker 22 which is rotatable by a shaft 24 cooperates in a known manner with the needle 14 to cause lock stitches to be formed in material 25 with the needle thread 20 and thread 26 supplied from a bobbin spool 27 rotatably mounted in a stationary bobbin case 28. A detailed description of the manner in which such a loop taker cooperates with a needle to form lock stitches may be found, for example, in U.S. Pat. No. 2,862,468 of R. E. Johnson for "Ornamental Stitch Sewing Machines" issued Dec. 2, 1958 and assigned to The Singer Company.

In accordance with the invention, a thead pulling bar 30 including a bobbin thread engageable leg 32 is provided to pull thread from the bobbin spool 27. Such thread pulling bar is mounted to pivot on an arm 34 which is an integral part of the bar and is rotatable in a fitting 36 located on a bed plate 38 that is secured by screws 40, 42 and 44 to machine frame 46. As shown, leg 32 of the thread pulling bar extends between spaced walls 45 and 47 provided on the bobbin case 28. Thread pulling bar 30 includes as an integral part thereof, an upwardly projecting angular extension 48 which is engageable by a pin 50 on a feed dog 52 that serves in the usual manner to move material being sewn in either a forward or reverse feeding direction when the needle is out of the work such that successive stitches may be formed.

The feed dog is moved, as usual, along a more or less elliptical path as determined by a work feed control system of the type shown and described, for example, in U.S. Pat. No. 3,527,183 for "Work Feeding Mechanism for Sewing Machines" of The Singer Company, issued Sept. 8, 1972. Such work feed control system includes a feed bar 54 mounted in the machine so that it may be oscillated in mutually perpendicular directions to impart substantially vertical and horizontal motion to the feed dog 52. The feed dog is carried by a bracket 56 which is secured to a pivot pin 58 journalled in the feed bar. A bed shaft 60, journalled in the machine frame and driven in synchronism with the needle actuating mechanism of the machine rotates an eccentric 62 and a lift cam 64. The lift cam imparts vertical motion to the feed bar through a bifurcated lever 66 pivoted on a fixed stud shaft 68, and through a link 70. Transverse feed motion is imparted to the feed bar by means of the eccentric 62, pitman 72, pivot pin 74, slide block 76, feed regulator block 78 and link 80. A vertical position of the feed regulator block 78 results in zero feed, whereas a clockwise position relative thereto as viewed in FIG. 3 results in the forward feeding of material and a stitch length which is in proportion to the clockwise displacement of the block 78 from the vertical. A counterclockwise position of the regulator block relative to the vertical results in the reverse feeding of material and a stitch length which is in proportion to the counterclockwise displacement of block 78 from the vertical. Regulator block 78 is positionable by shaft 82 which is in turn is positionable by manually operable stitch length selector 84.

In preparation for sewing, the bobbin case is threaded by drawing the thread 26 from the bobbin spool 27 through a slit 86 in the case 28, under a tension spring 88 and thence through a notch 90 in the case. Beyond the notch 90, bobbin thread 26 is passed over bobbin case wall 45, under leg 32 of the tread pulling bar, and over bobbin case wall 47, after which the thread is passed under cross piece 92 of the feed dog and up through an opening 94 in throat plate 95. Thread 22 after passing through a conventional thread tensioning device (not shown) and a take-up arm 96 is threaded through the eye 98 of needle 14.

The needle 14, loop taker 22 and feed dog 52 operate in timed relationship during sewing operations and lock stitches are formed in the usual manner, all as described in U.S. Pat. No. 2,862,468 (mentioned hereinbefore) except that bobbin thread is supplied for stitches during the forward feeding of material in accordance with the invention. Thread is pulled for forward stitching from bobbin spool 27 in successive increments of a length predetermined by the setting of regulator block 78 under the control of stitch length selector 84.

As the feed dog 52 moves upwardly in its travel and then forward, the bobbin thread 26 becomes taut and is caused to hold leg 32 of member 38 substantially at the level of the top of bobbin walls 45 and 47. Pin 50 on feed dog 52 moves toward angular extension 48 on member 32 as the feed dog moves forward. The angular extension 48 is contacted by the pin 50 and member 30 is pivoted downwardly by the pin during continued forward motion of the feed dog. Leg 32 moves downwardly and acts against the bobbin thread 26 causing it to be pulled from the spool 27 and into the space between bobbin walls 45 and 47. The extent to which member 30 is pivoted downwardly and the amount of thread which is pulled from the bobbin spool due to the forward movement of the feed dog is determined by the setting of regulator block 78 as disposed by stitch length selector 84. When the feed dog moves downwardly, member 30 is moved downward an additional distance substantially independent of the position of selector 84, by pin 50 and additional bobbin thread is drawn from the bobbin spool 27 by leg 32. Bobbin thread pulled from the spool 27 remains stored between bobbin case walls 45 and 47 until used in the formation of a stitch.

Beyond its lowest position, the feed dog 52 moves in a direction opposite to the work feeding direction and then upwardly after which it resumes movement in the work feeding direction. As the feed dog moves upwardly and during movement in the work feeding direction a stitch is set in the usual manner by operation of the needle thread takeup, and loose bobbin thread is drawn from between the walls 45 and 47 by the pull of a loop of needle thread on the bobbin thread. The bobbin thread which becomes taut pivots the thread pulling bar 30 upwardly and thereby repositions leg 32 enabling it to once again pull thread from the bobbin spool 27 as the feed dog moves further forward and then downwardly.

The net effect of the operation of the feed dog on thread pulling bar 30 is that bobbin thread is pulled during forward stitching from spool 27 in lengths controllable with manual selector 84. As made readily apparent in FIGS. 3 and 4 showing the feed dog in corresponding forward and down positions for selected short and long stitches respectively, short lengths of thread are drawn from the spool 27 for selected short stitches and long length of thread as drawn from the spool for selected long stitches, a proper length of thread for perfect stitches always being provided to prevent the puckering of material or the formation of inadequately locked stitches that easily pull out. During reverse stitching the pin 50 moves downwardly with the feed dog only while out of contact with angular extension 48, and is effective to depress bar 30 and cause thread to be pulled from spool 27 only in the latter portion of its forward motion. Therefore less bobbin thread in lengths dependent on selected stitch length is supplied during reverse stitching than in forward stitching. However, in reverse stitching it is usual to utilize short stitches and any additional thread required for the reverse stitches is pulled without the aid of thread pulling bar 30 directly from the spool by thread tension present during the formation of stitches, and no disadvantage results.

It is to be understood that the present disclosure relates to a preferred embodiment of the invention which is for purposes of illustration only, and that various modifications may be made therein without departing from the spirit and scope of the invention. 

I claim:
 1. In a lockstitch sewing machine, mechanism for removing lengths of thread from a bobbin spool for use in the formation of stitches by a needle including fixed thread supporting means between the bobbin spool and needle, a thread engageable member mounted in the machine for movement along an arcuate path and cooperable with the supporting means for pulling thread from the bobbin spool, an angular extension on said thread engageable member, a feed dog for moving material under the needle, means for moving the feed dog according to a selected length for stitches to be formed in the material, and a member affixed to the feed dog and engageable with said angular extension as determined by the motion of the feed dog whereby the thread engageable member is caused to pull lengths of thread from the bobbin spool in accordance with the selected stitch length.
 2. The combination of claim 1 including a manually operable selector for controlling the means for moving the feed dog according to the selected length for stitches to be formed in the material.
 3. The combination of claim 1 wherein the fixed thread supporting means is on a bobbin case which rotatably supports the bobbin spool.
 4. The combination of claim 3 wherein the fixed thread supporting means are spaced walls on the bobbin case, and the thread engageable means is operable to draw thread for stitches from the bobbin spool into the space between the thread supporting walls.
 5. The combination of claim 1 wherein the angular extension on the thread engageable member is an upwardly extending extension. 